Drug delivery devices have application where regular injection by persons without formal medical training occurs. This may be increasingly common among patients having diabetes where self-treatment enables such patients to conduct effective management of their disease. In practice, such a drug delivery device allows a user to individually select and dispense a number of user variable doses of a medicament.
There are basically two types of drug delivery devices: resettable devices (i.e., reusable) and non-resettable (i.e., disposable). For example, disposable drug delivery devices are supplied as self-contained devices. Such self-contained devices do not have removable pre-filled cartridges. Rather, the pre-filled cartridges may not be removed and replaced from these devices without destroying the device itself. Consequently, such disposable devices need not have a resettable dose setting mechanism.
A further differentiation of drug delivery device types refers to the dosing or drive mechanism: There are devices which are manually driven, e.g. by a user applying a force to an injection button, devices which are driven by a spring or the like and devices which combine these two concepts, i.e. spring assisted devices which still require a user to exert an injection force. The spring-type devices involve springs which are preloaded and springs which are loaded by the user during dose selecting. Some stored-energy devices use a combination of spring preload and additional energy provided by the user, for example during dose setting. Further types of energy storage may comprise compressed fluids or electrically driven devices with a battery or the like.
These types of delivery devices generally comprise of three primary elements: a cartridge section that includes a cartridge often contained within a housing or holder; a needle assembly connected to one end of the cartridge section; and a dosing section with the dosing mechanism connected to the other end of the cartridge section. A cartridge (often referred to as an ampoule) typically includes a reservoir that is filled with a medication (e.g., insulin), a movable rubber type bung or stopper located at one end of the cartridge reservoir, and a top having a pierceable rubber seal located at the other, often necked-down, end. A crimped annular metal band is typically used to hold the rubber seal in place. While the cartridge housing may be typically made of plastic, cartridge reservoirs have historically been made of glass.
The needle assembly is typically a replaceable double-ended needle assembly. Before an injection, a replaceable double-ended needle assembly is attached to one end of the cartridge section, a dose is set, and then the set dose is administered using the dosing mechanism of the dosing section. Removable needle assemblies may be threaded onto, or pushed (i.e., snapped) onto the pierceable seal end of the cartridge assembly.
The dosing section or dosing mechanism is typically the portion of the device that is used to set (select) a dose. During an injection, a plunger or piston rod contained within the dosing mechanism presses against the bung or stopper of the cartridge. This force causes the medication contained within the cartridge to be injected through an attached needle assembly. After an injection, as generally recommended by most drug delivery device and/or needle assembly manufacturers and suppliers, the needle assembly is removed and discarded.
The dosing section of drug delivery devices for selecting and dispensing a number of user variable doses of a medicament often comprises a display for indicating the selected dose to a user. This is especially important where a user may select a different dose each time depending on the state of health. There are mechanical displays, e.g. a drum with printed numbers on its outer surface, wherein the number corresponding to the actually selected dose is visible through a window or opening in the device.
A disposable drug delivery device is known from WO 2004/078241 A1, wherein the display comprises a number sleeve with numbers printed on its outer surface. The device further comprises a housing, a cartridge holder for retaining a cartridge containing a medicament, a piston rod displaceable relative to the cartridge holder, a driver coupled to the piston rod, a dose setting knob coupled to the driver and fixed to the number sleeve, and an injection button. The number sleeve is in threaded engagement with the housing, such that the number sleeve rotates along a helical path in a first direction during dose selecting and rotates back into the housing in a second, opposite direction during dose dispensing.